1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a sheet, and an image forming apparatus having such a sheet conveying apparatus.
2. Related Background Art
Conventionally, a sheet conveying apparatus for conveying an original, a copy sheet or the like has been used with an image forming apparatus such as a copying machine, a facsimile, a laser beam printer and the like.
In such a sheet conveying apparatus, it is required that a position of a sheet (particularly, a position of a leading end of the sheet) being conveyed is monitored for various reasons (for example, in order to stop the sheet being conveyed at a predetermined position (for example, when the sheet conveying apparatus is used for conveying an original in a copying machine, the original is stopped at a waiting position where the original is waited until a scanner becomes a readable condition or the original is stopped at an image reading position where the original is read), or, in order to effect any control at a timing when the sheet is conveyed to a predetermined position).
In order to monitor or grasp the leading end of the sheet being conveyed, although it is considered that sensors are disposed at predetermined positions (for example, in the vicinity of the waiting position or in the vicinity of the image reading position), in some cases, it is obliged that the sensors are arranged at upstream sides of the predetermined positions for various reasons (for example, problem regarding an installation space). In such cases, the position of the sheet has been grasped in the following methods:
(1) method in which a timing of passage of the xe2x80x9cleading endxe2x80x9d of the sheet is (detected by the sensor and the position is grasped on the basis of a conveying amount of the sheet after such timing; and
(2) method in which a timing of passage of the xe2x80x9ctrailing endxe2x80x9d of the sheet is detected by the sensor and the position of the leading end of the sheet is detected on the basis of a value obtained by adding a xe2x80x9clength of sheetxe2x80x9d to a xe2x80x9cconveying amount of the sheet after such timingxe2x80x9d.
Incidentally, in both methods (1) and (2), the conveying amount of the sheet is calculated on the basis of a signal from conveying means for conveying the sheet.
However, since the conveying amount of the sheet calculated on the basis of the signal from the conveying means includes any error more or less, when the above method (1) in which the conveying amount of the sheet is great is used, there arises a problem that grasp of the position of the sheet becomes incorrect.
On the other hand, when the above method (2) is used, since the conveying amount of the sheet is small in comparison with the above method (1), such a problem is reduced. However, if a sheet having a non-fixed size is conveyed, since it is difficult to detect a length of such a sheet correctly, any error is generated.
The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a sheet conveying apparatus in which a sheet having a fixed size and a sheet having a non-fixed size can be conveyed to a predetermined position correctly.
According to the present invention, there is provided a sheet conveying apparatus comprising sheet conveying means, detecting means for detecting passage of a sheet, and control means for controlling a sheet conveying amount of the sheet conveying means by the action of the detecting means to convey a leading end of the sheet to a predetermined position, and wherein the control means controls the sheet conveying amount in consideration of a length of the sheet on the basis of a timing when a trailing end of the sheet passes by the detecting means when the sheet has a fixed size and controls the sheet conveying amount on the basis of a timing when a leading end of the sheet passes by the detecting means when the sheet has a non-fixed size.
The present invention further provides a sheet conveying apparatus comprising original stacking means, feeding means for feeding originals on the original stacking means one by one, a first rotary member for further feeding the original to a reading position, a second rotary member for feeding the original fed by the first rotary member to read the original, reading means, detecting means disposed in the vicinity of the first rotary member to detect passage of the original, and control means for controlling an original conveying amount of the second rotary member by the action of the detecting means to stop a leading end of the original in a predetermined position of the reading position, and wherein the control means controls the original conveying amount in consideration of a length of the original on the basis of a timing when a trailing end of the original passes by the detecting means when the original has a fixed size and controls the original conveying amount on the basis of a timing when a leading end of the original passes by the detecting means when the original has a non-fixed size.
The present invention further provides a sheet conveying apparatus having conveying means for conveying a sheet, comprising size judging means for judging whether the sheet has a fixed size or a non-fixed size, length detecting means for detecting a length of the sheet in a conveying direction, sheet detecting means for detecting a timing of passage of a leading end of the sheet and a timing of passage of a trailing end of the sheet to generate a signal, conveying amount detecting means for receiving the signal from the sheet detecting means and for calculating a sheet conveying amount after the timing of passage of the leading end of the sheet or the timing of passage of the trailing end of the sheet, and conveying position calculating means for calculating a position of the leading end of the sheet conveyed at a downstream side of the sheet detecting means, and wherein, when it is judged that the sheet has the fixed size by the size judging means, the conveying position calculating means calculates the position of the leading end of the sheet on the basis of the sheet conveying amount after the timing of passage of the trailing end of the sheet calculated by the conveying amount detecting means and the length of the sheet in the conveying direction detected by the length detecting means, and, when it is judged that the sheet has the non-fixed size by the size judging means, the conveying position calculating means calculates the position of the leading end of the sheet on the basis of the sheet conveying amount after the timing of passage of the leading end of the sheet calculated by the conveying amount detecting means.
The present invention further provides an image forming apparatus comprising a sheet conveying apparatus for conveying an original, image reading means for reading an image on the original, and an image outputting portion for outputting the read image, in which the sheet conveying apparatus includes conveying means for conveying the original, size judging means for judging whether the original has a fixed size or a non-fixed size, length detecting means for detecting a length of the original in a conveying direction, sheet detecting means for detecting a timing of passage of a leading end of the original and a timing of passage of a trailing end of the original to generate a signal, conveying amount detecting means for receiving the signal from the sheet detecting means and for calculating an original conveying amount after the timing of passage of the leading end of the original or the timing of passage of the trailing end of the original, and conveying position calculating means for calculating a position of the leading end of the original conveyed at a downstream side of the sheet detecting means, and wherein, when it is judged that the original has the fixed size by the size judging means, the conveying position calculating means calculates the position of the leading end of the original on the basis of the original conveying amount after the timing of passage of the trailing end of the original calculated by the conveying amount detecting means and the length of the original in the conveying direction detected by the length detecting means, and, when it is judged that the original has the non-fixed size by the size judging means, the conveying position calculating means calculates the position of the leading end of the original on the basis of the original conveying amount after the timing of passage of the leading end of the original calculated by the conveying amount detecting means.
According to the feature of the present invention, both sheets having the fixed size and non-fixed size can be conveyed to the predetermined position correctly.